1. Field of the Invention
The present invention relates to a rewritable thermal label of the non-contact type. More particularly, the present invention relates to a method for recording and erasure of images using a rewritable thermal label of the non-contact type which enables rewriting images repeatedly in accordance with the non-contact method.
2. Description of Related Art
Currently, labels for control of articles such as labels attached to plastic containers used for transporting foods, labels used for control of electronic parts and labels attached to cardboard boxes for control of distribution of articles are mainly labels having a heat-sensitive recording material such as direct thermal paper as the face substrate. In the heat-sensitive recording material, a heat-sensitive recording layer containing an electron-donating dye precursor which is, in general, colorless or colored slightly and an electron-accepting color developing agent as the main components is formed on a support. When the heat-sensitive recording material is heated by a heated head or a heated pen, the dye precursor and the color developing agent react instantaneously with each other and a recording image is obtained. When an image is formed on the heat-sensitive recording material, in general, it is impossible that the formed image is erased and the condition is returned to that before the image is formed. However, the use of a rewritable label in which the heat-sensitive recording material allows erasure of images and rewriting of other images is recently increasing. When the label attached to an adherend is treated by rewriting without detaching the label from the adherend, the label attached to the adherend cannot be treated by passing through an ordinary printer for erasure of the recorded images and rewriting of other images. For this purpose, it is necessary that the erasure and the writing be performed in accordance with a method performed without contact.
Due to the above circumstances, in recent years, reversible heat-sensitive recording materials which allow recording and erasure of images for repeated use of a label, such as (1) a reversible heat-sensitive recording material having a heat-sensitive layer which is formed on a substrate and contains a resin and an organic low molecular weight substance showing reversible changes in transparency depending on the temperature and (2) a reversible heat-sensitive recording material having a heat-sensitive color development layer which is formed on a substrate and contains a dye precursor and a reversible color developing agent, have been developed. However, in the conventional rewritable thermal labels of the non-contact type, the erased image slightly remains without being completely erased during the repeated use. Due to the accumulation of the residual images, the contrast between the portion having recorded images and the portion having no recorded images decreases and problems arise on the visibility of characters and the readability of bar codes.
Patent reference 1: Japanese Patent No. 3295746